Journal of Arid Environments 135 (2016) 64e74
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Journal of Arid Environments
journal homepage: www.elsevier.com/locate/jaridenv
Population density of elephants and other key large herbivores in the
Amboseli ecosystem of Kenya in relation to droughts
Moses Makonjio Okello a, *, Lekishon Kenana b, Hanori Maliti c, John Warui Kiringe d,
Erastus Kanga b, Fiesta Warinwa d, Samwel Bakari c, Stephen Ndambuki b,
Edeus Massawe c, Noah Sitati e, David Kimutai c, Machoke Mwita c, Nathan Gichohi e,
Daniel Muteti b, Benard Ngoru b, Peter Mwangi b
a
Department of Tourism, Nairobi Campus, Moi University, P.O. Box 63056 - 00200, Nairobi, Kenya
Kenya Wildlife Service, P.O. Box 209949 - 003948, Nairobi, Kenya
c
Tanzania Wildlife Research Institute, P.O. Box 489357, Arusha, Tanzania
d
SFS Centre for Wildlife Management Studies, P.O. Box 27743 - 00506, Nairobi, Kenya
e
African Wildlife Foundation, P.O. Box 838484 - 3949, Nairobi, Kenya
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 November 2014
Received in revised form
15 August 2016
Accepted 20 August 2016
Kenya/Tanzania borderland is a critical area for conservation of biodiversity. This study was done to
establish the effects of 2007 and 2009 droughts through aerial counts. Findings indicate that large
mammal population collapsed, but some species crashed more than others. Total large mammal density
declined over three times (207.43%), recovering modestly (þ41.59%) between 2010 and 2013. Over that
time, the most abundant species was zebra (10,466.3 ± 2860.5 animals), followed by wildebeest
(8921.0 ± 4897.9), Grant's gazelle (3447.0 ± 303.7), Maasai giraffe (1381.3 ± 132.7), African elephant
(990.67 ± 12.60), eland (544.0 ± 311.4), Thomson's gazelle (495.3 ± 232.3), buffalo (331.3 ± 128.8) and
impala (354.3 ± 61.0). The species affected most by drought was lesser kudu, followed by African buffalo,
Maasai giraffe, kongoni, common eland, common wildebeest, common zebra, Grant's gazelle, gerenuk,
impala, African elephant, Thomson's gazelle and fringe - eared Oryx respectively. Further, large mammal
species numbers were dependent on location (c2 ¼ 13,647.35, df ¼ 15, p < 0.001), with numbers being
higher near protected areas. Animals with low numbers, specific diets, water - dependent and limited
range were most affected by the drought. This provides a baseline for future comparisons and also future
effects of droughts.
© 2016 Elsevier Ltd. All rights reserved.
Keywords:
Amboseli ecosystem
Distribution
Drought
Mortality
Population trends
1. Introduction
Wildlife conservation in Kenya began during the British colonial
rule and continued after independence in 1963. This has seen
nearly 8% of the country set aside for biodiversity conservation
purposes, and plans are underway to have additional landscapes
designated as wildlife conservation areas. This is in recognition of
the key role played by tourism in foreign revenue generation.
Although numerous strategies and financial resources have been
used to enhance wildlife conservation, there is rampant population
decline of numerous species throughout the country such as the
African elephant (Loxodonta africana), black rhino (Diceros bicornis),
* Corresponding author.
E-mail addresses: [email protected], [email protected] (M.M. Okello).
http://dx.doi.org/10.1016/j.jaridenv.2016.08.012
0140-1963/© 2016 Elsevier Ltd. All rights reserved.
gravy zebra (Equus grevyi), and large carnivores especially lion
(Panthera leo) and cheetah (Acynonix jubatus), various species of
monkeys, hilora antelope among others (Western et al., 2009a).
Numerous studies have examined the causes of decline of
wildlife populations in different parts of Kenya (e.g. Ottichilo et al.,
2000, 2001; Okello and Kiringe, 2004; Western et al., 2009a; b;
Primack, 1998). Collectively, these studies reveal that a myriad of
anthropogenic factors such as; human-wildlife conflicts, illegal
wildlife poaching, bush meat activities, increase in human population, alienation or inadequate involvement of locals in conservation initiatives and programs, proliferation of inappropriate land
uses like agriculture which compromise wildlife survival and its
conservation are responsible for the decline of wildlife. However,
the contribution of drought to wildlife decline has not been fully
evaluated yet its effects on populations can be devastating just like
M.M. Okello et al. / Journal of Arid Environments 135 (2016) 64e74
human related impacts. This article therefore focusses on the
impact of the 2007 to 2009 drought on elephants and other key
large mammalian wildlife species in the Amboseli Ecosystem of
Kenya.
In the last century, most parts of Kenya more so the high potential and heavily human populated have seen tremendous
decline and loss of large mammalian wildlife species. However, the
Amboseli Ecosystem, a semi-arid region, which until recently was
characterized by relatively low and sparse human population
(although now increasing because of immigrants and high birth
rates) is still endowed with diverse free ranging wildlife species.
Two major factors have interactively contributed to preservation of
wildlife in the ecosystem, elephants included; a semi-arid environment which acts as an ecological limitation to land use especially proliferation of rain-fed agriculture, lifestyle, culture and
traditions of the Maasai people who are the main inhabitants. The
foundation of the Maasai lifestyle is pastoralism which thrives in
relatively dry areas and allows livestock and wildlife to co-exist
which makes it compatible with wildlife conservation (Berger,
1993; Ntiati, 2002). Further, overtime, various taboos and traditional beliefs which abhors eating and indiscriminate killing of
wildlife among the Maasai has equally contributed to wildlife
preservation over the years (Seno and Shaw, 2002; Kangwana,
2011).
In the context of the Amboseli Ecosystem, the Amboseli National
Park which is the ecological lifeline of herbivorous wildlife species
is an important dry season concentration area for elephants and
other large wildlife species like common wildebeest (Connochaetes
taurinus), buffalo (Sycerus caffer) and common zebra (Equus
burchelli) (Western, 1975; Western and Maitumo, 2004; Croze and
Lindsay, 2011; Kangwana and Browne-Nunez, 2011). These species
also tend to spend nearly 80% of their time outside the park and use
a landscape about 20 times bigger than the park (Croze and Moss,
2011). Studies have therefore demonstrated that these species
move seasonally in and out of the park (Western, 1975; Esikuri,
1998; Kioko, 2005; Croze and Lindsay, 2011), but are currently
living in a rapidly evolving human matrix characterized by enormous land use, tenure and increasing human population growth as
a result of immigrants overflowing from fertlile arable lands, and
increasing local birth rates (Okello and Kioko, 2010; Kangwana and
Browne-Nunez, 2011). This poses an immediate and future threat to
the survival and conservation of wildlife in the entire ecosystem
(Western, 1982; Kangwana and Browne-Nunez, 2011).
The population of elephants in the ecosystem which is currently
estimated at nearly 1500 individuals (Croze and Lindsay, 2011) was
nearly exterminated in the 1980s due to poaching. Moss (2011)
estimated that in the early 1970's, the elephant population in the
entire ecosystem was about 600 individuals and due to the relative
safety accorded to them, the population rapidly increased, and by
the end of 2002, it stood at nearly 1225 individuals. It's one of the
best-studied wild elephants in Kenya and the world, as a result of
work of Cynthia Moss and her collaborators over the last 30 years.
The population once extended from Ol Donyo Orok in the west to
the Chyulu Hills in the east, near the town of Emali in the north, and
to the slopes of Mt. Kilimanjaro in the south (Western and Lindsay,
1984). During the 1990s and into the last century, the range has
begun to expand again. Consequently, considerable efforts have
gone into encouraging the Amboseli elephants to disperse more
widely outside the park by working towards greater tolerance
amongst local communities.
The future and long term conservation of elephants and other
wildlife types in the Amboseli region depends not only on maintaining the ecological integrity of Amboseli National Park and
adjoining areas but also enlisting the support of the Maasai who
live beyond the park boundaries. However, there are concerns that
65
the park's integrity and consequently its ability to support elephants and populations of other large herbivores like zebra and
wildebeest has increasingly been compromised by long term
vegetation changes. For the last 50 years or so, the yellow acacia
woodlands have significantly declined and are nearly absent in
most parts of the park, and this has created a lot of concern among
conservationists and wildlife management authorities in the
country (Western and Maitumo, 2004; Western, 2006).
In their 20 years research work in the park, Western and
Maitumo (2004) demonstrated that loss and impaired regeneration of Acacia woodlands in the park was largely attributed to impacts associated with elephants. Subsequent studies (Western,
2006) further revealed tremendous changes in vegetation within
the park characterized by decline and loss of woody vegetation
communities and expansion of grassland and scrubland. This has in
turn put a lot of ecological pressure on the swamps through herbivory and trampling effects of large aggregations of elephants,
zebra and wildebeest particularly during the dry season when their
dispersal is reduced. Another concern regarding the future of the
park is the effects if climate change and rainfall variability (Fig. 1).
Thompson et al. (2009) noted that the glaciers and relief rainfall of
Mt. Kilimanjaro are the major source of water for the Amboseli
swamps, but climate change effects on water sources are affecting
the volume of these swamps. This is also being accelerated by the
logging and general deforestation on Mt. Kilimanjaro. The short and
long term ecological damage associated with environmental
change can't be underestimated, and calls for crafting of well
thought and sound management strategies that will reduce significant deterioration of the park. Thus, every effort should be made
to ensure the landscape adjoining the park is secured and both
elephants and other migratory species are able to use them as has
been the tradition.
Another concern in the borderland is the emergence of agriculture especially in the Amboseli Ecosystem, which was introduced in the last century by immigrants from other parts of Kenya
plus the Chagga people from Tanzania (Esikuri, 1998; Ntiati, 2002;
Okello, 2005; Okello and D'Amour, 2008). The ecological ramifications and threats posed by this new land use continues to cause a
lot of concern among conservationists and wildlife conservation
NGOs working in the region. Seno and Shaw (2002) have described
the emergence of a diverse community of farmers, ranchers, and
entrepreneurs in areas like the Amboseli as the biggest challenge to
the future of wildlife conservation. Further, the push and general
clamor for sub-division of the group ranches will have irreversible
negative impacts on elephants and other species alike and will
negatively affect wildlife survival and conservation efforts, and this
Fig. 1. Rainfall trends in the Amboseli Ecosystem (1977e2012). Source.Kenana et al.,
2013
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M.M. Okello et al. / Journal of Arid Environments 135 (2016) 64e74
has become the single most important threat to wildlife, elephants
included (Croze et al., 2006).
Globally, the percentage of land under drought has risen
dramatically in the last 25 years, and the incidents of drought, both
short and long term, has been rising in Africa (Conway, 2008),
including the Amboseli region (Thompson et al., 2009). Given the
arid to semi-arid nature of the region, droughts can lead to massive
mortality of wildlife especially water dependent species and those
which require large amounts of daily food intake. In this regard,
during the 2007 to 2009 there were two severe droughts in the
Kenya/Tanzania borderland (land encompassing Kilimanjaro, West
Kilimanjaro, Lake Natron and Lake Magadi area) that had one of the
most severe effects in history because of their proximity and impacts on large mammals and livestock. The Kenya/Tanzania
borderland represents one of the most important conservation
areas in the world, having large free wild mammals roaming between Kenya and Tanzania and having renowned national parks
(Amboseli, Kilimanjaro, Maasai Mara and Serengeti). It therefore
represents an important conservation area in the world. The two
droughts in the region may have been some of the most severe in
history due to impact and proximity, and so provided an opportunity to examine the influence of droughts on elephants and other
key large herbivorous wildlife species, based on data collected
during the dry season and within two droughts between 2007 and
2009.
The overall objective was to estimate the changes in elephant
and other large herbivore density associated with droughts and
make inferences about this for large mammal conservation. Specifically, we addressed the following objectives:i. Determine the population status elephants and key large
herbivorous wildlife species in the Amboseli Ecosystem
ii. Assess the effects of the 2007 to 2009 drought on the population of elephants and key large herbivorous wildlife species in the Amboseli Ecosystem
ii. Establish the distribution pattern of elephants and other
large wildlife species in the Amboseli Ecosystem
iv. Make appropriate recommendation for management
2. Materials and methods
2.1. The 2008 to 2011 drought and its impacts in Kenya
According to NOAA (2008), drought is a deficiency in precipitation over an extended period, usually a season or more, resulting
in a water shortage causing adverse impacts on vegetation, animals,
and/or people. It is a normal, recurrent feature of climate that occurs in virtually all climate zones, from very wet to very dry.
Drought is a temporary aberration from normal climatic conditions,
thus it can vary significantly from one region to another. Drought is
different than aridity, which is a permanent feature of climate in
regions where low precipitation is the norm, as in a desert.
This large mammal count was done at a time when there were
two severe droughts in the Kenya/Tanzania borderland (PDNA,
2011). For the entire country, rainfall fell below the monthly
average in 8 months out of 12, or 67 percent of the time in 2008. In
2009, the number of months showing less rainfall than the longterm monthly average increased to 9 or 75 per cent of the time.
In 2010, the number of rainfall deficit months decreased to 7.5
months (62 percent of the time); and in the first half of 2011, the
number of months rose significantly to 5 out of 7 months (72
percent of the time) (PDNA, 2011).
The overall impact of the 2008e2011 droughts in Kenya is
estimated at Ksh 968.6 billion (US$12.1 billion). This includes Ksh
64.4 billion (US$805.6 million) for the destruction of physical and
durable assets, and Ksh 904.1 billion (US$11.3 billion) for losses in
the flows of the economy. The most affected sector was livestock
(Ksh 699.3 billion), followed by agriculture (Ksh 121.1 billion). The
highest values of per capita damage and losses occurred in provinces where the HDI is lowest. The economic impact of the drought
is estimated to have slowed down the growth of the country's
economy by an average of 2.8 percent per year across Kenya (PDNA,
2011; NOAA, 2008).
2.2. Study area
Amboseli region is situated in the Southern part of Kenya, and
covers an area of approximately 8797 Km2 (Fig. 2). It's made up of
several blocks of land, mainly; Amboseli National Park, and Maasai
owned group ranches (Olgulului/Olararashi, Eselenkei/lengisim,
Mbirikani, Kuku, Kaputei, Osilalei, Mailua and the former Kimana/
Tikondo Group Ranch. It also includes former 48 former ranches,
located on the lower slopes of Mt. Kilimanjaro along the international border with Tanzania, that are currently subdivided and
under rain-fed agriculture (Fig. 2). The region consists of basement
plains, saline plains with fresh water swamps and the volcanic
slopes of Mt. Kilimanjaro. Quaternary volcanic soils on the northeastern Kilimanjaro slope dominate around the southeast, which
favors crop production while the southeast part of Ilkisongo is
covered by basement rock soils making it largely suitable for
pastoralism (Pratt and Gwynne (1977).
The Amboseli area lies in ecological zone VI, and is generally arid
to semi-arid savanna environment with low agricultural potential
(Pratt and Gwynne, 1977; Croze et al., 2006). It's characterized by
spatial and temporal variation in hydrology, and surface water is
only found in few permanent streams and rivers (Fig. 1). The
streams, rivers and existing water resources are predominantly a
result of the hydrological influence of Mt. Kilimanjaro, where water
flows underground and emerges elsewhere in the form of streams,
rivers or swamps (Ntiati, 2002). These springs together with rainfall, feed the rivers, streams and swamps in the area.
Rainfall in the Amboseli region is mostly bimodal, but its unpredictable and unreliable in amount and timing (Ntiati, 2002). The
short rains occur between the end of October and mid-December,
while the long rains fall between March and May (Okello and
D'Amour, 2008), and the mean annual rainfall across the area
ranges from 400 to 1000 mm (Reid et al., 2004). The OctobereDecember rainfall accounts for 45%, and the MarcheMay for
30% of the total rainfall received. Therefore, the amount of rainfall is
the single most important factor influencing land use practices,
which currently include agriculture, pastoralism and wildlife conservation (Ntiati, 2002). Human population growth in the region
especially within the group ranches and along the slopes of Mt.
Kilimanjaro has been rapid, and population in the area more than
doubled between 1979 and 1999 (Reid et al., 2004). Over the past 15
years the number of registered members within the Kimana, Kuku,
and Mbirikani Group Ranches has increased by 505%, 1323%, and
497%, respectively (Ntiati, 2002). This rapid population increase is
due to the immigration of non-pastoral people seeking access to
more productive land within the group ranches (Ntiati, 2002). At
the same time, the land within the group ranches has experienced
extensive changes over the past 30 years in response to a variety of
economic, cultural, political, institutional, and demographic processes (Reid et al., 2004). Pastoralism, which was once the backbone of the Maasai livelihood, has declined tremendously, partly as
a result of increased agricultural activities that have become
widespread in the entire region (Ntiati, 2002).
The vegetation of the region is typical of a semi-arid environment. Dominant vegetation types are: open grasslands towards the
M.M. Okello et al. / Journal of Arid Environments 135 (2016) 64e74
67
Fig. 2. Location and outline of the Amboseli Ecosystem.
north and northeast to the Chyulu Hills, Acacia dominated bushland southward to the forest belt of Mt. Kilimanjaro. In these main
types, there are patches of swamps and swamp-edge grasslands
and Acacia woodlands.
3. Methods
Total aerial counts of elephants and key large herbivorous
wildlife species were conducted during the dry season in 2007
(24th to 29th May at the start of rain season), 2010 (11th to 16th
October at the end of dry season) and 2013 (6th to 12th October)
based on the technique described by Norton-Griffiths (1978). The
count therefore employed the Global Positioning System (GPS)
technique with Arc View software used for plotting species distribution maps. Counts were done within blocks demarcated based on
well-defined ground features such as; roads, rivers, hills etc. (Fig. 3),
in an average area of 7852 km2. These features were meant to make
it easier for pilots to navigate the blocks, thus the counting blocks
design was demarcated so as to conform to the following rules; i)
rivers were not used as boundaries of the blocks. Rivers are normally areas of concentration of animals hence not suitable as
boundaries for counting blocks owing to the necessity to turn over
this area and begin a new transect and the high possibility animals
would move from one side of the river to the other, resulting in
double counts, ii) blocks were made rectangular or square in shape,
which eased navigation for the pilots and Front Seat Observer (FSO)
using GPS and allowed more time for observations, iii) blocks were
made small enough to be counted within a maximum of 6 h a day,
and an area of 900 km2 was deemed a suitable average size of a
block, and, iv) block boundaries did not cut across areas of high
wildlife density as determined by kernel densities from previous
surveys.
To improve the quality of data collected on wildlife populations,
the crew was trained in the use of various counting and estimation
techniques, use of GPS equipment, voice recorders and cameras),
species identification and estimation, data handling and processing. Practical training sessions and test flights were included as
rehearsal for the actual census. The test flights involved the
different flight crews flying the same mock transects at different
intervals while maintaining same orientation in order to assess
inter observer variability in species detection, estimation and
identification. Thereafter, each block was systematically searched
68
M.M. Okello et al. / Journal of Arid Environments 135 (2016) 64e74
Fig. 3. Counting blocks and flight paths used during census.
using light air-crafts flying either North South or East West directions along transects of 1e2 km width depending on visibility
and terrain (Fig. 3). The aircraft crew consisted of a pilot, Front Seat
Observer (FSO) and Rear Seat Observer (RSO). The aircraft crew
systematically searched for and made observations and recording
of elephants and key large wildlife species and their number along
the flight transects. For each observation a waypoint was marked
using a hand held Global Positioning System (GPS) and the observation recorded on a data sheet. Tape recorders were also used to
aid in data capture and data were transcribed into the datasheet
after every survey session. Large herds of more than 10 individuals
were photographed unless the view was obstructed by thick
vegetation, in order to establish the correct count (DouglasHamilton, 1996). At the end of each count session, the GPS flight
paths and waypoints were downloaded using DNR-Garmin/
MapSource software (Minesota Department of Natural Resources),
and the FSO did a summary table of each block. Any double counts
in neighboring blocks were also validated worked out and eliminated during these sessions. Voice recordings were processed
digitally to remove background noises and improve clarity. A team
of data handlers transcribed the voice records onto datasheets and
entered these into a digital database. The exercise started every
morning at around 7:30 a.m. and ended in the afternoon. End time
was variable because it depended on the size of the blocks, and rest
breaks were taken during refueling of the aircrafts at lunch time.
Flight path and way point data were processed using ArcGIS 9.3
(ESRI, Redlands California) program, while the observation data
sheets were cleaned and entered into Microsoft Excel 2003/2007
for further analysis.
3.1. Data analysis
Data for the dry period of 2007 (during the drought, which
ended in 2009 in Amboseli area) and then after droughts (2010 and
2013) were used. Tallies, percentages, means and standard errors
for the data were calculated using standard statistical methods (Zar,
1999) using PASW version 18 (SPSS Inc.). CJhanges in population
numbers were expressed as percent change in 2007 and 2013
relative to 2010 population counts. Chi e square cross e tabulations
were done to establish the association between species numbers
and the counting areas (group ranch locations), and between species numbers and years (association to drought periods) using
PASW statistical software. Even though the dry season census area
of the year 2007 was 5542 km2 mainly in Amboseli Ecosystem, the
census area increased to 8797 km2 in 2010 and further to 9212 km2
in 2013 to cover the entire Kenya/Tanzania borderland. The total
numbers may therefore be affected by the size, but the density and
proportions of each species of the large mammals seen were
M.M. Okello et al. / Journal of Arid Environments 135 (2016) 64e74
reliable measures for comparison due to weighting per unit area
and as a proportion. Even though the cross e tabulations may be
affected because of the slight study site size differences especially
between 2010 and 2013, in our view, this was deemed not to greatly
alter the general conclusions of that test. However, the same study
area size would be most appropriate for comparisons especially for
cross tabulations. However, we recognize that this could be a limitation of the chi e square cross e tabulation comparisons.
4. Results
Changes in numbers of elephants in between 2007 and 2010,
and between 2010 and 2013 was expressed as percent to calculate
the percent changes in density between the years. The general
overall large mammal average density declined more than three
times (207.45%) between 2007 and 2010, and recovered only
modestly between 2010 and 2013 (Table 1). The common large
mammal species numbers were dependent (c2 ¼ 5988.60, df ¼ 10,
p < 0.001) on the period in relation to the drought (during the
drought in 2007, just after the drought in 2010, and well after the
drought in 2013). Generally, large mammal numbers declined
during the drought until after the drought ended, with most of
them recovering in post drought period. Further, the numbers of
large mammal species was dependent (c2 ¼ 13,647.35, df ¼ 15,
p < 0.001) on relative location from protected areas, with numbers
being higher to areas close to a protected area (Amboseli, Tsavo
West, Chyulu Hills), but lower in areas further away from protected
areas (like Eselenkei and parts of Olgulului/Ololorashi Group
Ranch).
The African elephant (Loxodonta Africana) was the fifth most
abundant species in overall density (Table 1) over the three years
(Fig. 4). It had an average number comprising about 4% of all the
counted large mammal species (Table 1). The drought was associated with declining elephant density and numbers from 2007.
The most abundant large mammal species (based on overall
density) over this period (Table 1) were common zebra (Equus
burchelli) followed by common wildebeest (Chonochaetus taurinus),
Grant's gazelle (Gazella granti), Maasai giraffe (Giraffa carmelopardalis), African elephant, common eland (Taurotragus Oryx),
Thomson's gazelle (Gazella thomsoni), impala (Aepyceros melampus), African buffalo (Cyncerus caffer) and lesser kudu (Tragelophus imberbis) respectively.
Based on overall density, the most abundant wildlife species
among those surveyed was the common zebra (Table 1). It
comprised about 38% of all the counted large mammals over that
time (Fig. 5). Zebra density also declined during the drought from
2007 to 2010, but recovered in density between 2010 and 2013
(Table 1).
The second abundant large mammal species in overall density
was the common wildebeest (Fig. 6). It comprised about 27% of
large mammals counted (Table 1). During the drought, the common
wildebeest declined sharply between 2007 and 2010. However, its
population recovered remarkably from 2010.
Grant's gazelle was the third most abundant large mammal
species in overall density. It comprised about 14% of counted large
mammals (Table 1). The species declined also during the drought as
well as after drought ended. Its population declined sharply in
population density between 2007 and 2010, and continued to
decline still after drought between 2010 and 2013.
The fourth abundant large mammal species in overall density
was the Maasai giraffe. It comprised about 5% of large mammals
counted (Table 1). During the drought, the Maasai giraffe declined
in density in 2010, but had a positive increase in density after the
drought between 2010 and 2013.
The sixth abundant large mammal in overall density was the
69
common eland. It comprised about 2% of all large mammals seen
(Table 1). The eland declined sharply in density between 2007 and
2010. However, the species started making positive recovery after
this time.
The seventh abundant large mammal species in overall density
was the Thomson's gazelle. It comprised only about 2% of large
mammal counted (Table 1). The Thomson's gazelle density declined
during the drought between 2007 and 2010, but recovered between 2010 and 2013.
Impala comprised only 1% of all the large mammals counted
between 2007 and 2013 (Table 1). They declined in between 2007
and 2010, but recovered between 2010 and 2013. Similarly, African
buffalo, which had a low density (Table 1) declined sharply during
the drought between 2007 and 2010. The decline continued even
after drought ended.
Lesser kudu had also a low density (Table 1) as it comprised less
than 1% of large mammals counted (Table 1). They declined sharply
in density during the drought. But after the drought, the density
had a positive recovery. Similarly, Kongoni (Coke's hartebeest,
Alcelaphus buselaphus) had a low density (Table 1). Its density
declined during the drought, and further continued to decline in
density even after the drought ended (Table 1).
Lastly, two species with eve low population densities were
gerenuk (Litocranius walleri) and fringe e eared Oryx (Oryx buselaphus). Gerenuk declined during the drought, but made a very
modest positive recovery in density after the drought ended.
Similarly, the Fringe e eared Oryx also declined in density during
the drought, but had a positive recovery in density by almost the
same amount as the Oryx after the drought ended (Table 1).
In terms of the most drastic decline in overall density during the
drought, the species order with most decline in density was lesser
kudu followed by Maasai giraffe, common wildebeest, common
eland, common zebra, African buffalo, Thomson's gazelle, impala,
fringe e eared Oryx, kongoni, gerenuk, Grant's gazelle and African
elephant respectively. Looking at the rate of recovery in density
between 2010 and 2013, the poorest recovery in density was in
kongoni density followed by African buffalo, African elephant,
Grant's gazelle, gerenuk, lesser kudu, Maasai giraffe, impala, common eland, common zebra, wildebeest and lastly fringe e eared
Oryx respectively. Based on a combined rate of decline during the
drought (between 2007 and 2010) and recovery after droughts
(between 2010 and 2013), the species with lowest overall rate was
lesser kudu, followed by African buffalo, Maasai giraffe, kongoni,
common eland, common wildebeest, common zebra, Grant's gazelle, gerenuk, impala, African elephant, Thomson's gazelle and
lastly fringe e eared orxy respectively. But one species that seemed
not affected by drought of 2007e2009 was the African hippopotamus (Hippopotamus amphibius) which maintained a low density
but increased in density during the drought as well as after the
drought between 2010 and 2013.
Some carnivores were also seen in the 2007 and 2013 census,
albeit smaller numbers and low densities. These included the African lion (Panthera leo), the spotted hyena (Crocuta crocuta) and
the cheetah (Acinonyx jubatus). The spotted hyena seemed to be the
relatively most abundant followed by the lion and lastly the
cheetah (Table 1).
5. Discussion
The African elephant is an important ecological keystone for the
African Savanna. It has been ranked as “Vulnerable” by the International Union for Conservation of Nature (IUCN) (Blanc, 2008)
although individual population segments are ranked as “Endangered” (central Africa), “Vulnerable” (western Africa, eastern Africa)
and “Least Concern” (southern Africa). Other than poaching,
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M.M. Okello et al. / Journal of Arid Environments 135 (2016) 64e74
Table 1
Population size and density of elephants and other wildlife species from 2007 to 2013.
Large mammal
Year
Census
area (km2)
Number
Percent abundance
in area
Density per km2
(Mean ± SE)
Abundance rank based on
overall density (and % change before
and after drought)
African elephant
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
2013
Overall
2007
2010
5542
8797
9214
967
1010
995
990.67 ± 12.60
588
222
184
331.33 ± 128.90
1458
1053
1444
1318.33 ± 132.73
1161
162
309
544.00 ± 311.40
15,328
5424
10,647
10,466.33 ± 2860.47
18,538
2499
5726
8921.00 ± 4897.90
102
71
27
66.67 ± 21.76
84
49
139
90.67 ± 26.19
220
21
35
92.00 ± 64.13
10
43
70
41.00 ± 17.35
736
630
488
618.00 ± 71.84
4054
3126
3161
3447.00 ± 303.67
396
152
938
495.33 ± 232.27
426
233
404
354.33 ± 61.00
112
84
90
95.33 ± 8.51
60
0
13
24.33 ± 18.22
1
e
5
3.00 ± 1.63
12
e
2.18
6.83
4.02
4.34 ± 1.35
1.33
1.50
0.74
1.19 ± 0.23
3.29
7.12
5.84
5.41 ± 1.12
2.62
1.09
1.25
1.65 ± 0.48
34.61
36.66
43.03
38.10 ± 2.54
41.86
16.89
23.14
27.30 ± 7.50
0.23
0.48
0.11
0.27 ± 0.11
0.19
0.33
0.56
0.36 ± 0.11
0.50
0.14
0.14
0.26 ± 0.12
0.02
0.29
0.28
0.20 ± 0.09
1.66
4.26
1.97
2.63 ± 0.82
9.15
21.13
12.78
14.35 ± 3.55
0.89
1.03
3.79
1.90 ± 0.94
0.96
1.57
1.63
1.39 ± 0.21
0.25
0.57
0.36
0.39 ± 0.09
0.14
0.00
0.05
0.06 ± 0.04
0.00
e
0.02
0.01 ± 0.01
0.00
e
0.17
0.11
0.11
0.13
0.11
0.03
0.02
0.05
0.26
0.12
0.16
0.18
0.21
0.02
0.03
0.09
2.77
0.62
1.16
1.51
3.35
0.28
0.62
1.42
0.02
0.01
0.00
0.01
0.02
0.01
0.02
0.01
0.04
0.00
0.00
0.02
0.00
0.00
0.01
0.00
0.13
0.07
0.05
0.09
0.73
0.36
0.34
0.48
0.07
0.02
0.10
0.06
0.08
0.03
0.04
0.05
0.02
0.01
0.01
0.01
0.01
0.00
0.00
0.00
0.00
e
0.00
0.00
0.00
e
5 (35.29, 0.00)
African buffalo
Maasai giraffe
Common eland
Common zebra
Common wildebeest
Coke's hartebeest (kongoni)
Fringe e eared Oryx
Lesser kudu
African hippopotamus
Maasai Ostrich (game bird)
Grant's gazelle
Thomson's gazelle
Impala
Gerenuk
Olive baboon
African lion
Spotted hyena
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
9214
(Mean)
5542
8797
± 0.02
9 (72.73, 33.33)
± 0.03
4 (53.85, þ33.33)
± 0.04
6 (90.48, þ50.00)
± 0.06
1 (77.62, þ87.11)
± 0.65
2 (91.64, þ121.43)
± 0.97
12 (-50.00, 100.00
± 0.00
12 (50.00, þ50.00)
± 0.00
11 (100.00, 0.00)
± 0.01
15 (0.00, þinfinity)
± 0.00
6 (-46.15, 28.57
± 0.02
3 (þ50.68, 5.56)
± 0.13
8 (71.43, þ50.00)
± 0.02
9 (62.50, þ33.33)
± 0.01
12 (þ50.00, 0.00)
± 0.00
15 (100.00, þinfinity)
± 0.00
15
± 0.00
15
M.M. Okello et al. / Journal of Arid Environments 135 (2016) 64e74
71
Table 1 (continued )
Large mammal
Cheetah
Total for only large mammals
between 2007 and 2013
Year
Census
area (km2)
Number
Percent abundance
in area
Density per km2
(Mean ± SE)
2013
Overall (Mean)
2007
2010
2013
Overall (Mean)
9214
3
7.50 ± 3.67
2
e
1
1.50 ± 0.41
0.01
0.01 ± 0.01
0.00
e
0.00
0.00 ± 0.00
0.00
0.00 ± 0.00
0.00
e
0.00
0.00 ± 0.00
43,550
14,165
24,253
27,322.45 ± 8620.45
7.86
1.61
2.63
4.03 ± 1.93
53.13
17.28
29.59
33.33 ± 10.52
2007
2010
2013
Overall (Mean)
5542
8797
9214
5542
8797
9214
Abundance rank based on
overall density (and % change before
and after drought)
15
Percent change in density
e
67.47
þ12.64
Fig. 4. Distribution of the African elephant during the dry season of 2013.
droughts are one of the most significant mortality factors for elephants. Droughts, especially if frequent and intense, are always
accompanied by reduced access to water and vegetation and also
face relatively higher heat load from increased temperature. All
these affect the survival and reproduction of elephants, and eventually its population status. This drought was also accompanied by
elephant mortality as well as decline in numbers and density.
Droughts have caused significant mortality in elephant populations
in historic times, such as in Tsavo National Park from 1960 to 1961
and from 1970 to 1975 (Spinage, 1994). All these factors reduce
elephant population and affect rate of recovery of the population
after droughts.
The African elephant is a water-dependent species, with requirements of 150e300 L of water per animal per day for drinking,
with additional amounts required for bathing (Du Toit, 2002a,b;
Garai, 2005). Therefore acquisition of water is a significant part of
their daily activity, although they may go for three days without
drinking in wet season (Spinage, 1994). Elephants can walk up to
30e50 km or more in search of water (Spinage, 1994; Garai, 2005).
They readily dig for water in dry riverbeds if surface water is not
available (Garai, 2005). Further, under drought conditions,
competition for forage and water with people and livestock
increased human-elephant conflicts leading to both human and
elephant mortality (Muruthi, 2005). Poaching, crop raiding, water
use and other conflicts with humans will increase as elephant
forage and water resources reduce during drought.
Elephants are heat-sensitive animals and individual elephants
are susceptible to heat stress and sunburn generated from between
1 and 2 C in temperature change (Du Toit, 2002b; Garai, 2005).
Elephants manage their body temperature through physiological
mechanism such as heat dissipation through their ears; behavioral
mechanisms such as mud baths, water baths, spraying of water
through the trunk onto the body and seeking shade (Spinage, 1994;
Garai, 2005). Climate change such as droughts may also be associated with elephant diseases that reduce their body condition.
Elephants are sensitive to diseases such as anthrax, trypanosomiasis, encephalo-myocarditis, salmonellosis, endotheliotropic herpes, foot-and-mouth disease and floppy trunk disease (Du Toit,
2002b; Garai, 2005), which are exacerbated by drought and heat
stress.
72
M.M. Okello et al. / Journal of Arid Environments 135 (2016) 64e74
Fig. 5. Distribution of common zebra during the dry season of 2013.
Fig. 6. Distribution of common wildebeest during the dry season of 2013.
However, elephants are extremely adaptable, occupying a variety of habitats from desert to savanna to gallery forest (Lausen and
Bekoff, 1978). In savanna ecosystems, they also tend to select where
and what to feed on in order to maximize rate of nutrient intake
which enhances their survival and reproduction chances in times of
limited food quantity and quality (Lindsay, 2011). Further, they
normally spend more time browsing during dry spells (Jachmann,
1989; Kangwana, 1993; Lindsay, 2011). Their forage also tends to
M.M. Okello et al. / Journal of Arid Environments 135 (2016) 64e74
be diverse and may include herbs bark, fruits, tree forage and grass
(Kangwana, 1993; Western, 1975; Estes, 1992; Croze and Lindsay,
2011; Kioko, 2005). Thus, the feeding behavior of elephants confers them a significant amount of ecological survival advantage
over many other wildlife species when faced by prolonged drought
conditions.
All wild large mammals (and equally livestock from observation
on the ground) were affected by the 2007 to 2009 droughts, leading
to declines in their density. Large mammal numbers underwent
drastic population decline in the study area during 2007 and 2009.
Two of the most abundant grazing species in the area: zebra and
wildebeest showed the highest declines, but also the highest recovery rates after the droughts. The degree of decline and recovery
was dependent on large mammal abilities to migrate, vary feeding
patterns, ability to cope with heat and rise in temperature, ability to
change forage preference and the population size maintained
during and before the droughts. Understanding the factors influencing the recovery rates of these different species after a major
population decline is vital to predicting whether species will persist
in the future, in the face of anthropogenic pressures and climate
change.
Differential response of animals to droughts can also arise
because of their social behavior and foraging strategies. Duncan
et al. (2012) suggested that the species most at risk from drought
are those relatively sedentary, and those wholly or partially
dependent on plants less resistant to droughts. This is further
compounded by intense intra and inter-species competition for
reduced forage during droughts with other species (Estes, 1992).
Grazers may survive droughts better than browsers because
browse declines during droughts faster than grass (Western, 1975).
And this confers grazers an ecological advantage over bowsers
when faced by food shortages during the dry season or in times of
drought. Lesser kudu and Maasai giraffe are pure browsers (Estes,
1992), but also had very low density in the study area, which
makes them extremely vulnerable to droughts because of initial
low numbers and dependence on browse that rapidly declines
during droughts.
The common zebra is a bulk feeder and a hind-gut fermenter,
and can therefore utilize grass forage of low quality (Rubenstein,
2010) unlike other grazers like the common wildebeest. Further,
its grass forage tends to have more stem than leaf material unlike
the wildebeest (Estes, 1992), conferring it some ecological advantage in utilizing grass forage. Rubenstein (2010) noted that abundant food and water supply normally reduces competition between
different reproductive groups of common zebra females.
Animals who are already too low in number are likely to
continue to decline even though conditions (of plenty of water and
pasture) improve due to demographic Allee’ effect (a depressed
population condition due to few breeding numbers in the population) (Allee et al., 1949; Berec et al., 2001). The lesser kudu,
gerenuk, hartebeest, and oryx had very low population numbers
and so they are likely to decline further due to their population
being generally lower than minimum viable size to allow for a more
rapid population increase once drought conditions improve. So
whether a large mammal population has high fecundity, natality
and generally reproductive potential, the level to which populations are reduced by droughts will affect their ability to cope
with droughts (Gandiwa et al., 2016).
However, this study didn't evaluate other key factors such as
range degradation, livestock overgrazing and competition with
wild large mammals and human persecution such as poaching and
snaring for bush meat that may have contributed to wildlife mortality and population decline. However, numerous studies in semiarid savannas of Africa including the Amboseli region have reported
wildlife decline commonly attributed to growth of agro-pastoral
73
populations, livestock and subsistence and commercial agriculture (Homewood et al., 2001). In this regard, it's probable that such
factors may have contributed significantly to mortality and associated decline of wildlife besides actual drought effects in the 2007
to 2009 drought in the borderland. For hundreds of years, the human population in the ecosystem remained quite low but from the
middle of the last century, and at the beginning of the new one, the
population escalated drastically. This has been accompanied by all
manner of changes including sedentarization and associated
infrastructure development, group ranch subdivision land use
changes such as farming and land privatization (Kimani and
Pickard, 1998; Ntiati, 2002; Western et al., 2009b) which negatively affects wildlife. Western et al. (2009a) revealed a significant
decline and loss of wildlife inside and outside Kenya's protected
areas which they attributed to a combination of factors including
loss of range and migratory routes due to human activities. Ottichillo et al. (2000) examined the population trends of large nonmigratory wildlife herbivores in the Maasai Mara Ecosystem between 1977 and 1997, and their findings showed that they had
declined by 58%. They attributed this to a combination of poaching,
drought, vegetation and land use changes.
Another factor that may have equally contributed to the
observed mortality is high stocking rate for livestock and as associated deterioration in range condition in the Amboseli Ecosystem.
Recent studies (Kiringe and Okello, 2010, 2012) have revealed
widespread poor state of the rangelands in the ecosystem characterized by decline and loss of Decreaser grasses, prevalence of forbs,
Increaser II grasses and soil erosion, decline in herbaceous vegetation cover, and poor forage potential. These changes could be as a
result of a various factors but ecologically they indicate that the
ability to produce sufficient food resources that can support large
populations of herbivores has declined over the years. Consequently, in the event of a prolonged drought, food quantity and
variety available to animals will become very scarce leading to
starvation and death.
While land use changes, habitat loss and degradation have been
identified as key threats to wildlife in the Amboseli Ecosystem,
climate variability and associated occurrence of drought present a
major environmental challenge to wildlife conservation. This calls
for sustained monitoring of the status and trends of wildlife populations whilst isolating the underlying causes for the observed
patterns so as to help formulate appropriate strategies for better
conservation practices. Drought is also a threat to Maasai pastoral
lifestyle which is the backbone of their livelihood and similarly,
appropriate interventions that will help them sustain this practice
amidst a dry and rapidly changing landscape are urgently needed.
Acknowledgements
This work is a collective effort of various persons and institutions. In particular, we sincerely thank the Director of the
Kenya Wildlife Services (KWS), Director General of Tanzania
Wildlife Research Institute (TAWIRI), Director Amboseli Trust for
Elephants (ATE), Director of Wildlife Division (Tanzania) and Director General of Tanzania for providing staff, equipment, vehicles
and aircrafts during the census. We also applaud and acknowledge
the hard work done by the pilots, survey observers, GIS specialists
and data handlers, ground crew and other support personnel
without whom the census would not have been successful.
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